1. Field of the Invention
The present invention relates to a temperature detection circuit using temperature characteristics of a semiconductor circuit.
2. Description of the Related Art
FIG. 11 illustrates a conventional temperature detection circuit.
The temperature detection circuit includes a positive power supply terminal 001, a negative power supply terminal 002, a reference voltage circuit 200, a temperature sensor circuit 300, a comparator 400, and an output terminal 700.
A negative pole of the reference voltage circuit 200 is connected to the negative power supply terminal 002 and a positive pole of the reference voltage circuit 200 as an output terminal 101 is connected to an inverting input terminal of the comparator 400. The reference voltage circuit 200 outputs, at a predetermined temperature, a reference voltage which is equal to an output voltage of the temperature sensor circuit 300.
The temperature sensor circuit 300 includes a constant current source 310 and a diode 320. One end of the constant current source 310 is connected to the positive power supply terminal 001 and the other end of the constant current source 310 is connected to an anode of the diode 320. A cathode of the diode 320 is connected to the negative power supply terminal 002. The anode of the diode 320 as an output terminal 100 is connected to a noninverting input terminal of the comparator 400 and outputs a voltage which is lowered according to a temperature rise.
An output terminal of the comparator 400 is connected to the output terminal 700 of the temperature detection circuit. The comparator 400 compares the reference voltage from the reference voltage circuit 200 and the output voltage of the temperature sensor circuit 300, and, according to the result of the comparison, outputs a negative power supply potential or a positive power supply potential.
Next, operation of the temperature detection circuit is described.
V100 in FIG. 12 is the voltage at the output terminal 100 of the temperature sensor circuit 300 while V101 is the voltage at the output terminal 101 of the reference voltage circuit 200. When the temperature is lower than a predetermined temperature, because the output voltage V100 is higher than the reference voltage V101, the comparator 400 outputs the positive power supply potential. When the temperature is higher than the predetermined temperature, because the output voltage V100 of the temperature sensor circuit 300 is lower than the reference voltage V101, the comparator 400 outputs the negative power supply potential. In this way, the temperature detection circuit switches the output logic state at the predetermined temperature, and thus, the predetermined temperature can be detected (see Japanese Patent No. 3139194).
Here, although the reference voltage V101 is adjusted to be equal to the output voltage V100 of the temperature sensor circuit 300 at the predetermined temperature, even after the adjustment, a dispersion ΔV illustrated in the figure is caused.
The dispersion ΔV in the reference voltage V101 causes a dispersion ΔT in the detected temperature in the temperature detection circuit. Therefore, in the conventional temperature detection circuit, by imparting negative temperature characteristics to the constant current source 310 or by increasing the number of the diodes 320 connected in series, the temperature gradient of the output voltage V100 is made steep to attempt to suppress the influence of the dispersion ΔV in the reference voltage V101 on the dispersion ΔT in the detected temperature.
In a temperature detection circuit, when the temperature to be detected is changed, it is general that the characteristics of the temperature sensor circuit 300 is not changed but the reference voltage V101 of the reference voltage circuit 200 is changed.
However, in the temperature detection circuit described above, as illustrated in FIG. 13, with regard to two predetermined temperatures Tx and Ty, the reference voltage V101y at Ty which is lower than Tx is higher than the reference voltage V101x. More specifically, there is a problem in that, the larger the range of the set predetermined temperature becomes toward the lower temperature side, the higher the output voltage V100 and the reference voltage V101 become, and the lowest operating voltage of the temperature detection circuit becomes higher. Conversely, when a temperature sensor circuit having a positive temperature gradient is used, there is a problem in that, the larger the range of the set predetermined temperature becomes toward the higher temperature side, the higher the output voltage V100 and the reference voltage V101 become, and the lowest operating voltage of the temperature detection circuit becomes higher.